As low sulfur natural gas fields are being depleted, gas production from other sources is necessary to meet today's energy demands. With increasing energy costs, gas production from high acid gas natural gas fields and syngas production via gasification of carbonaceous materials are becoming economically attractive. High acid gas fields and coal mines are still plentiful in many parts of the world. However, due to the relatively high carbon contents of these resources, CO2 emissions from gas processing plants using these resources are often unacceptably high and generally require CO2 capture and sequestration.
Most typically, the CO2 content in high acid gas fields ranges from about 10 mol % to about 50 mol %, which is entirely unsuitable to meet pipeline specifications (e.g., 1 to 2 mol % CO2 and 4 ppmv H2S). Similarly, syngas or hydrogen production from gasification has often unacceptably high acid gas content, which necessitates removal and sequestration of CO2 to minimize greenhouse gas effects. Unfortunately, sequestration of CO2 requires compression to a very high pressure (e.g., 2000 psig or higher), which is energy intensive, especially where CO2 is produced at or near atmospheric pressure from conventional gas treating processes. Typical examples for such CO2 generation and sequestration are provided in U.S. Pat. No. 7,192,468 and WO 2004/052511, which are incorporated by reference herein. While such plants and methods are relatively effective in CO2 removal from high-pressure feed gases, the produced CO2 is at or near atmospheric pressure and so requires substantial expenditure of energy for injection into the formation. Similarly, certain configurations for heating and flashing the heated solvent to about atmospheric pressure to recover CO2 is known from U.S. Pat. Nos. 3,664,091 and 3,594,985, but once again produce a low-pressure CO2 product that requires substantial recompression. Thus, and viewed from a different perspective, all or almost all of the known configurations and methods for acid gas removal produce a treated gas at high pressure and a CO2 stream at close to atmospheric pressure.
In similar configurations and methods, as for example described in WO 2007/077137, a sequential flash process for a heated physical solvent is used where the solvent is flashed to a relatively low pressure (less than 200 psi), and where the solvent is heated using steam. While such configurations reduce the energy demand for CO2 recompression at least to some degree, a relatively large demand for energy is required for the generation of steam used in the solvent heating. Such high energy demand is equally known for processes where sequential flashing of an amine solvent at high temperatures is performed as described in U.S. Pat. No. 5,061,465.
Thus, although various configurations and methods are known to remove acid gases from different feed gases, all or almost all of them suffer from one or more disadvantages. For example, all or almost all of the known processes tend to require significant heating in solvent regeneration, and the recovered CO2 typically requires significant compression as the CO2 is at or near atmospheric pressure. Therefore, there is still a need to provide improved methods and configurations for acid gas removal.